John Stachowicz's favourites

John Stachowicz is a community ecologist based at the University of California, Davis. His works centres on the interactions among species and how they contribute to both the maintenance of species diversity and the consequences of diversity loss for ecosystem functioning. His primary experimental work focuses on marine systems, and encompasses a broad range of habitat types and taxa such as macroalgae, marine plants, sessile and mobile invertebrates. He has selected four articles from volume 4 of Biology Letters.

"In the past few issues, Biology Letters has published a number of papers relevant to natural and anthropogenic threats to marine ecosystems. I have selected several of these papers that I think represent innovative approaches or reveal or underline important findings. There were more great papers than I have room to highlight here, and I hope that this will serve as a way to highlight that Biology Letters has become an outlet for rapid publication of important basic and applied papers in the marine biological sciences. Because this is a journal that crosses the Biological Sciences, the papers I have selected represent a diversity of approaches, including articles written from a biomechanical, population genetic, ecological and fisheries management perspectives."

A threat to coral reefs multiplied? Four species of crown-of-thorns starfish

"A long-standing puzzle in pacific coral reef systems is the cause of the episodic outbreaks of the crown of thorns starfish (Acanthaster planci), which eats live coral tissue, having a devastating effect on infested reefs that rivals the most notorious insect pests on land. In this paper, the authors use mitochondrial DNA markers to show that what was previously thought to be a single species ranging across the Indo-Pacific ocean is comprised of four genetically distinct, and geographically restricted, clades. Severe outbreaks apparently occur mostly in the geographic range inhabited by one of the "species" (the Pacific), suggesting that lineage-specific studies of the ecology and behaviour may be required to develop a fuller understanding of these reef pests."

Abstract
In the face of ever-increasing threats to coral reef ecosystems, it is essential to understand the impact of natural predators in order to devise appropriate management strategies. Destructive population explosions of the crown-of-thorns starfish Acanthaster planci have devastated coral reefs throughout the Indo-Pacific for decades. But despite extensive research, the causes of outbreaks are still unclear. An important consideration in this research is that A. planci has been regarded as a single taxonomic entity. Using molecular data from its entire distribution, we find that A. planci is in fact a species complex. This discovery has important consequences for future coral reef research, and might prove critical for successful reef conservation management.

"This paper integrates biomechanical models of coral resistance to storm waves with predictions of changing coral strength due to dropping ocean pH under global change scenarios, to predict changes in the species composition of corals on reefs. Specifically, highly branched forms are predicted to suffer from weakening structural support, giving way to smaller and mechanically more robust species. Because many species of fish and invertebrates use the structurally complex branching species as habitat, this finding suggests that changes in coral composition due to increased storm intensity and/or ocean acidification would result in declines in the diversity and abundance of reef associated species. These declines in diversity could further reduce the resilience of reefs, rendering them increasingly susceptible to other threats."

Abstract
Increasingly severe storms and weaker carbonate materials associated with more acidic oceans will increase the vulnerability of reef corals to mechanical damage. Mechanistic predictions based on measurements of colony mechanical vulnerability and future climate scenarios demonstrate dramatic shifts in assemblage structure following hydrodynamic disturbances, including switches in species' dominance on the reef and thus potential for post-disturbance recovery. Larger colonies are more resistant to factors such as disease and competition for space, and complex morphologies support more associated reef species. Future reefs are thus expected to have lower colony abundances and be dominated by small and morphologically simple, yet mechanically robust species, which will in turn support lower levels of whole-reef biodiversity than do present-day reefs.

"The authors provide a novel field test of the effects of ocean acidification by comparing the community of epibionts on seagrasses in areas with lowered pH near volcanic vents that naturally emit CO2 into the ocean with nearby areas of normal pH. They find that a drop in pH similar in magnitude to that expected under some global change scenarios resulted in the virtual disappearance of assemblages of calcified epibionts on seagrass leaves. This field-based approach is novel a welcome complement to the acute-stress, lab-based experiments on consequences of ocean pH change conducted to date."

Abstract
Surface ocean pH is likely to decrease by up to 0.4 units by 2100 due to the uptake of anthropogenic CO2 from the atmosphere. Short-term experiments have revealed that this degree of seawater acidification can alter calcification rates in certain planktonic and benthic organisms, although the effects recorded may be shock responses and the long-term ecological effects are unknown. Here, we show the response of calcareous seagrass epibionts to elevated CO2 partial pressure in aquaria and at a volcanic vent area where seagrass habitat has been exposed to high CO2 levels for decades. Coralline algae were the dominant contributors to calcium carbonate mass on seagrass blades at normal pH but were absent from the system at mean pH 7.7 and were dissolved in aquaria enriched with CO2. In the field, bryozoans were the only calcifiers present on seagrass blades at mean pH 7.7 where the total mass of epiphytic calcium carbonate was 90 per cent lower than that at pH 8.2. These findings suggest that ocean acidification may have dramatic effects on the diversity of seagrass habitats and lead to a shift in the biogeochemical cycling of both carbon and carbonate in coastal ecosystems dominated by seagrass beds.

The dangers of ignoring stock complexity in fishery management: the case of the North Sea cod

"This paper points out that many fish species that are treated as panmictic are, in fact, comprised of genetically distinct subpopulations and explores the implications of this for the management of fisheries. While the paper focuses on the North Sea Cod as an example, it draws evidence from other species as well. The author highlights how genetically-based phenotypic diversity among fish subpopulations in their response to environmental variation can buffer the overall catch against changes in the environment. The author warns that failure to consider genetic distinctness of subpopulations within managed species can, however, lead to the crash of particular populations and urges stronger consideration of population genetic structuring in fisheries management."

Abstract
The plight of the marine fisheries is attracting increasing attention as unsustainably high exploitation levels, exacerbated by more extreme climatic conditions, are driving stocks to the point of collapse. The North Atlantic cod (Gadus morhua), a species which until recently formed a major component of the demersal fisheries, has undergone significant declines across its range. The North Sea stock is typical of many, with a spawning stock biomass that has remained below the safe biological limit since 2000 and recruitment levels near the lowest on record. Cod within the North Sea are currently managed as a single stock, and yet mounting empirical evidence supports the existence of a metapopulation of regionally variable, genetically distinct, sub-stocks. Applying the same management strategies to multiple stocks that differ in their resilience to exploitation inevitably results in the overfishing and likely collapse of the weaker components. Indeed, recent studies have identified two North Sea spawning stocks that have undergone disproportionally large collapses with very substantial reductions in egg production. Similarly affected cod stocks in the northwest Atlantic have shown little evidence of recovery, despite fishery closures. The possible implications of ignoring sub-structuring within management units for biocomplexity, local adaptation and ecosystem stability are considered.